1. Field of the Invention
The invention relates to a method of estimating motion of objects in successive animated images subdivided into two-dimensional blocks scanned in accordance with a predetermined sequence in each image, said method comprising the steps of determining a set of error data and, based on this set, estimating a motion vector for each current block of one of the successive images with respect to blocks of the preceding image within a search window.
The invention also relates to a device for performing this method.
A motion vector is to be understood to mean a vector characterizing the shift of the current block with respect to a block of the preceding image in the sequence and having the closest luminosity properties of the current block.
The invention is used in the field of television, in image coding systems and for various television standards, for example, for conventional television, high-definition television, or for the American or European system, etc.
2. Description of the Related Art
A motion estimation device is already known from Patent Specification GB 2,214,751. This Specification describes a method referred to as "Block Matching Process" or motion estimation method by correspondence of blocks. In this method, denoted BMA (Block Matching Algorithm) hereinafter, a search of a corresponding block is effected in the image which precedes the current image and in a neighborhood of given dimensions marked by a window referred to as the search window, which dimensions are related to a maximum amplitude of the searched motion vector. The corresponding block is the block which, in accordance with predetermined criteria, has the luminosity properties which are most similar to those of the current block.
The drawback of the known BMA process is that it provides non-coherent motion vectors. Non-coherence is to be understood to mean that in the image, which is decomposed into blocks, the probability that neighboring blocks have either the same motion vector or a vector of close value is very small. The result is that the effects of subdivision into blocks appear during reconstitution of the image on the basis of these non-coherent motion vectors, which effects consist of discontinuities at the borders of blocks which do not have identical motion vectors.